Early detection of cancer or its recurrence is tantamount to a good health outcome. Identifying markers that surface at an early stage allow the oncologist to more successfully treat the cancer patient.
Immune suppressor cells, such as myeloid-derived suppressor cells (MDSC), contribute to tumor immune tolerance and the failure of immunotherapy regimens in cancer patients and experimental tumor models (1). MDSC reportedly inhibit T cell effector functions through a range of mechanisms, including: arginase 1 (ARG-1)-mediated depletion of L-arginine (2); inducible nitric oxide synthase (iNOS) and NADPH oxidase (NOX2) production of reactive nitrogen and oxygen species (3, 4); vascular endothelial growth factor over-expression (5); cysteine depletion (6); and the expansion of T-regulatory (Treg) cell populations (7, 8). While rare or absent in healthy subjects, MDSC accumulate in the settings of trauma, severe infection or sepsis, and cancer (9), possibly as a result of the hypoxic environment and hypoxia-inducible factor (HIF)-1α expression (10). MDSC have been described in patients with colon carcinoma (11), melanoma (11), hepatocellular carcinoma (12), head and neck squamous cell carcinoma (4), non-small cell lung carcinoma (13), renal cell carcinoma (14), pancreatic adenocarcinoma (15) and breast carcinoma (16). In cancer patients, Diaz, et al. (16) propose that accumulation of MDSC correlates with more advanced disease and poor prognosis. The ability to detect characteristic MDSC in cancer patients would allow the oncologist to determine the effectiveness of therapy and if tumor recurrence has occurred after treatment. Furthermore, MDSC characterization in peripheral blood could be used to differentiate between benign and malignant lesions and masses which can be difficult to discern by routine imaging, fine needle aspiration biopsies, or existing serum assays. Thus, there is a need in the art for methods of identifying MDSC populations so that the appropriate treatment regimine can be prescribed. This invention satisfies this need and provides related advantages as well.